// Cellular noise ("Worley noise") in 2D in GLSL.
// Copyright (c) Stefan Gustavson 2011-04-19. All rights reserved.
// This code is released under the conditions of the MIT license.
// See LICENSE file for details.
// https://github.com/stegu/webgl-noise

// Cellular noise, returning F1 and F2 in a vec2.
// Speeded up by using 2x2 search window instead of 3x3,
// at the expense of some strong pattern artifacts.
// F2 is often wrong and has sharp discontinuities.
// If you need a smooth F2, use the slower 3x3 version.
// F1 is sometimes wrong, too, but OK for most purposes.
vec2 cellular2x2(vec2 P) {
#define K 0.142857142857 // 1/7
#define K2 0.0714285714285 // K/2
#define jitter 0.8 // jitter 1.0 makes F1 wrong more often
        vec2 Pi = mod289(floor(P));
        vec2 Pf = fract(P);
        vec4 Pfx = Pf.x + vec4(-0.5, -1.5, -0.5, -1.5);
        vec4 Pfy = Pf.y + vec4(-0.5, -0.5, -1.5, -1.5);
        vec4 p = permute(Pi.x + vec4(0.0, 1.0, 0.0, 1.0));
        p = permute(p + Pi.y + vec4(0.0, 0.0, 1.0, 1.0));
        vec4 ox = mod7(p)*K+K2;
        vec4 oy = mod7(floor(p*K))*K+K2;
        vec4 dx = Pfx + jitter*ox;
        vec4 dy = Pfy + jitter*oy;
        vec4 d = dx * dx + dy * dy; // d11, d12, d21 and d22, squared
        // Sort out the two smallest distances
#if 0
        // Cheat and pick only F1
        d.xy = min(d.xy, d.zw);
        d.x = min(d.x, d.y);
        return vec2(sqrt(d.x)); // F1 duplicated, F2 not computed
#else
        // Do it right and find both F1 and F2
        d.xy = (d.x < d.y) ? d.xy : d.yx; // Swap if smaller
        d.xz = (d.x < d.z) ? d.xz : d.zx;
        d.xw = (d.x < d.w) ? d.xw : d.wx;
        d.y = min(d.y, d.z);
        d.y = min(d.y, d.w);
        return sqrt(d.xy);
#endif
}
